I've had this problem before, where I connect my laptop to my Panasonic plasma TV thru the HDMI connector. When I had Ubuntu 8.10 (Jaunty), I managed to fix the problem with this thread: http://ubuntuforums.org/showthread.php?t=1077801
Now I have Ubuntu 10.04 (Lucid). Everything is updated, I have nvidia drivers 254, I've also updated Alsa to 188.8.131.52. I was having trouble getting audio to sound proper in the headphone jack, but I was only getting the rear surround channel (no voices, only soundtrack).
Everything should be mixed down on the fly to stereo L-R, and I should have possible routing to the headphones, the built-in speakers, and the HDMI. But I do NOT have anything in the HDMI.
Audio is in Pulseaudio, and working (I see the VUmeters on screen and they are active). Just not in the HDMI.
Is there anything I should be looking for in terms of config? I know my way around Ubuntu, but somehow I think I must be missing this one